Activation of Inflammasomes Requires Intracellular Redistribution of the Apoptotic Speck-Like Protein Containing a Caspase Recruitment Domain

Bryan, Nicole B.; Dorfleutner, Andrea; Rojanasakul, Yon; Stehlik, Christian

doi:10.4049/jimmunol.0802367

Cited by 229 publications

(238 citation statements)

References 59 publications

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“…5B and C, top). This agrees with data from previous studies that showed that both ASC and caspase-4 are stimulated during L. pneumophila infection of human macrophages (59,60), although our data are the first documentation of the role of ASC and caspase-4 in IL-6 secretion. The knockdown of ASC or caspase-4 did not decrease the ratio of the IL-6 output from mutant-infected cells to that from WT-infected cells (Fig.…”

Section: Resultssupporting

confidence: 81%

The Type II Secretion System of Legionella pneumophila Dampens the MyD88 and Toll-Like Receptor 2 Signaling Pathway in Infected Human Macrophages

2017

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Previously, we reported that mutants of Legionella pneumophila lacking a type II secretion (T2S) system elicit higher levels of cytokines (e.g., interleukin-6 [IL-6]) following infection of U937 cells, a human macrophage-like cell line. We now show that this effect of T2S is also manifest upon infection of human THP-1 macrophages and peripheral blood monocytes but does not occur during infection of murine macrophages. Supporting the hypothesis that T2S acts to dampen the triggering of an innate immune response, we observed that the mitogen-activated protein kinase (MAPK) and nuclear transcription factor kappa B (NF-B) pathways are more highly stimulated upon infection with the T2S mutant than upon infection with the wild type. By using short hairpin RNA to deplete proteins involved in specific pathogen-associated molecular pattern (PAMP) recognition pathways, we determined that the dampening effect of the T2S system was not dependent on nucleotide binding oligomerization domain (NOD)-like receptors (NLRs), retinoic acid-inducible protein I (RIG-I)-like receptors (RLRs), double-stranded RNA (dsRNA)-dependent protein kinase receptor (PKR), or TIR domain-containing adaptor inducing interferon beta (TRIF) signaling or an apoptosis-associated speck-like protein containing a CARD (ASC)-or caspase-4-dependent inflammasome. However, the dampening effect of T2S on IL-6 production was significantly reduced upon gene knockdown of myeloid differentiation primary response 88 (MyD88), TANK binding kinase 1 (TBK1), or Toll-like receptor 2 (TLR2). These data indicate that the L. pneumophila T2S system dampens the signaling of the TLR2 pathway in infected human macrophages. We also document the importance of PKR, TRIF, and TBK1 in cytokine secretion during L. pneumophila infection of macrophages.KEYWORDS Legionella pneumophila, TLR2, cytokine, innate immunity, macrophage, type II secretion L egionella pneumophila, a Gram-negative bacterium that is widespread in aquatic habitats, is the principal agent of Legionnaires' disease pneumonia (1-6). In the lungs, Legionella bacteria invade and grow in resident macrophages and then trigger severe inflammation (2). In macrophages, L. pneumophila evades the degradative lysosomal pathway and replicates to large numbers within a membrane-bound vacuole, the Legionella-containing vacuole (LCV) (7,8). Two protein secretion systems, Lsp type II secretion (T2S) and Dot/Icm type IV secretion (T4S), play major roles in the pathogenesis of L. pneumophila (9, 10). In T2S, protein substrates are first translocated across the inner membrane, and upon the action of the T2S pilus-like apparatus, they then exit the bacterial cell through a specific outer membrane pore (11). Using proteomics and enzymatic assays, we have shown that the T2S system of L. pneumo-

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Section: Resultssupporting

confidence: 81%

The Type II Secretion System of Legionella pneumophila Dampens the MyD88 and Toll-Like Receptor 2 Signaling Pathway in Infected Human Macrophages

2017

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“…We observed that in WT BMDMs, treatment with LPS or ATP for 15 min led to relocalization of ASC from the nucleus to the cytosol (SI Appendix, Fig. S8), as has been reported previously (20) Fig. S8).…”

Section: Irak-1 Associates With Inflammasome Components and Regulatessupporting

confidence: 69%

“…S8). On inflammasome activation, oligomerized ASC forms specks in the cells, representing assembled inflammasome complexes (20). We observed speck formation by ASC only when cells were exposed to both LPS and ATP, and this formation was significantly more pronounced in WT BMDMs compared with IRAK-1 KO BMDMs (Fig.…”

Section: Irak-1 Associates With Inflammasome Components and Regulatesmentioning

confidence: 79%

IRAK-1 bypasses priming and directly links TLRs to rapid NLRP3 inflammasome activation

Lin

Troutman

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

242

205

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Significance Toll-like receptors recognize conserved molecules that are expressed by both harmless (commensal) and harmful (virulent) microbes. Another set of receptors, nucleotide-binding oligomerization domain-like receptors (NLRs), are expressed in the cytosol and recognize virulence factors and toxins from pathogenic microbes. Previous studies on TLRs and NLRs have suggested that TLR signaling primes the NLR inflammasome pathway. Here we discovered that TLRs, via the signaling molecule IL-1 receptor-associated kinase, directly regulate activation of a specific NLR, nucleotide binding and oligomerization, leucine-rich repeat, pyrin domain-containing 3 (NLRP3). This is important because when infection occurs, the virulent/pathogenic microorganisms activate both of these receptors. We also found that simultaneous activation of TLRs and NLRP3 is important for rapid innate immune response by the host.

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“…Stable THP-1shASC (ASCdef THP-1) cells were previously generated by lentiviral transduction with pLKO.1-based vectors (ASC sequence 5=-GCTCTTCAGTTTCACACC A-3= and a nontargeting control sequence [Sigma]). Envelope and packaging plasmids were produced in HEK293T cells by puromycin selection (25,26). THP-1 cells deficient in NLRP3 (NLRP3def THP-1) were purchased from InvivoGen and cultured in supplemented RPMI as described above, with 200 g/ml hygromycin added at every other passage, in accordance with the manufacturer's instructions.…”

Section: Methodsmentioning

confidence: 99%

Mechanisms of Inflammasome Activation by Vibrio cholerae Secreted Toxins Vary with Strain Biotype

et al. 2015

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Activation of inflammasomes is an important aspect of innate immune responses to bacterial infection. Recent studies have linked Vibrio cholerae secreted toxins to inflammasome activation by using murine macrophages. To increase relevance to human infection, studies of inflammasome-dependent cytokine secretion were conducted with the human THP-1 monocytic cell line and corroborated in primary human peripheral blood mononuclear cells (PBMCs). Both El Tor and classical strains of V. cholerae activated ASC (apoptosis-associated speck-like protein-containing a CARD domain)-dependent release of interleukin-1␤ (IL-1␤) when cultured with human THP-1 cells, but the pattern of induction was distinct, depending on the repertoire of toxins the strains produced. El Tor biotype strains induced release of IL-1␤ dependent on NOD-like receptor family pyrin domain-containing 3 (NLRP3) and ASC due to the secreted pore-forming toxin hemolysin. Unlike in studies with mouse macrophages, the MARTX toxin did not contribute to IL-1␤ release from human monocytic cells. Classical biotype strains, which do not produce either hemolysin or the MARTX toxin, activated low-level IL-1␤ release that was induced by cholera toxin (CT) and dependent on ASC but independent of NLRP3 and pyroptosis. El Tor strains likewise showed increased IL-1␤ production dependent on CT when the hemolysin gene was deleted. In contrast to studies with murine macrophages, this phenotype was dependent on a catalytically active CT A subunit capable of inducing production of cyclic AMP and not on the B subunit. These studies demonstrate that the induction of the inflammasome in human THP-1 monocytes and in PBMCs by V. cholerae varies with the biotype and is mediated by both NLRP3-dependent and -independent pathways. V ibrio cholerae is the causative agent of the diarrheal disease cholera. The O1 serogroup, which is most associated with disease, is divided into two biotypes, classical and El Tor. Classical strains were responsible for the six cholera pandemics that occurred during the 19th century and the first half of the 20th century and are noted for their severe clinical presentation. In 1961, the El Tor strains emerged as the cause of the ongoing seventh pandemic, completely displacing the classical strains from the environment and as a cause of cholera in humans (1). These strains colonize the intestine more effectively and spread between hosts more efficiently but cause fewer deaths and significantly more asymptomatic colonization (2).The primary virulence factor for pandemic cholera strains is cholera toxin (CT), an ADP-ribosylating toxin that disables the G␣ s subunit, resulting in increased cyclic AMP (cAMP) production and secretion of fluid from enterocytes due to the opening of chloride channels. The toxin is composed of the catalytically active A (CTA) subunit associated with five CTB subunits that bind to surface GM 1 gangliosides, facilitating toxin endocytosis (3). In addition to enterotoxigenic activity, CT has also been demonstrated to have immunomodulat...

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Activation of Inflammasomes Requires Intracellular Redistribution of the Apoptotic Speck-Like Protein Containing a Caspase Recruitment Domain

Cited by 229 publications

References 59 publications

The Type II Secretion System of Legionella pneumophila Dampens the MyD88 and Toll-Like Receptor 2 Signaling Pathway in Infected Human Macrophages

The Type II Secretion System of Legionella pneumophila Dampens the MyD88 and Toll-Like Receptor 2 Signaling Pathway in Infected Human Macrophages

IRAK-1 bypasses priming and directly links TLRs to rapid NLRP3 inflammasome activation

Mechanisms of Inflammasome Activation by Vibrio cholerae Secreted Toxins Vary with Strain Biotype

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